Immunity to trypanosomatids species

ABSTRACT

The present invention relates to trypanosomatid histones in substantially isolated form for use as a protective antigen against trypanosomatid infection. These histones may be either isolated from the corresponding parasite or be produced by means of recombinant DNA techniques. For the latter purpose the invention also provides genes encoding histones and derivatives of the genes like other nucleic acids and gene products like peptides and proteins. The invention further provides diagnostic tests, pharmaceutical compositions and vaccines comprising the usual excipients and/or adjuvants and at least one histone, a histone encoding gene or a derivative thereof.

[0001] The present invention relates to genes and corresponding gene products (DNAs, RNAs and proteins) for use in vaccines and diagnostics specific for intracellular infectious agents, in particular for parasite infection, more in particular for trypanosomatids infection, in particular for Leishmania species infection, more in particular for cutaneous lesions inducing Leishmania, more in particular for Leishmania major.

[0002] Leishmania, a member of the trypanosomatid family, is endemic in the tropical regions of America, Africa and the Indian subcontinent, in the sub-tropics of south-west Asia and in the Mediterranean. Infection with different species of the protozoan Leishmania, which is transmitted by sandflies, manifests itself as either self-healing cutaneous lesions, as neurological and cardiac disorders or as fatal visceral infections. The disease caused by Leishmania is generally called leishmaniasis.

[0003] Some forms of the disease are anthroponotic (transmitted only between humans), while others are zoonotic (involving a human reservoir). There are over 20 known species of Leishmania of which a dozen are associated with the various forms of leishmaniasis.

[0004] Based on the clinical pattern, the leishmaniasis can be classified into three groups. Cutaneous leishmaniasis is the most prevalent, producing skin ulcers which may take more than a year to heal. Mucocutaneous leishmaniasis initially causes similar lesions which may heal but reappear to cause hideous tissue destruction, primarily the nose and the mouth. Finally, visceral leishmaniasis is a very severe systemic disease which is nearly always fatal if left untreated.

[0005] Since the mid-1980s a dramatic increase in the number of opportunistic Leishmania infections has been reported with the spread of the HIV epidemy to areas traditionally endemic for leishmaniasis. Currently the world wide prevalence of leishmaniasis is 12 million cases (see review Liew and O'Donnell, 1993) and 350 millions live in risk areas. The number of new cases of the disease each year being of the order of 1.5 million, of which 500.000 are visceral leishmaniasis.

[0006] Visceral leishmaniasis causes large scale epidemics and the number of cases varies greatly between the years. During 1991 there were large epidemics in India and Sudan. The number of cases in India alone may have been of the order of 250.000. It is estimated that visceral leishmaniasis may have killed 75.000 people in 1991.

[0007] The impact of cutaneous leishmaniasis is less dramatic, but it causes severe suffering in endemic areas, not least because of the social and psychological trauma associated with disfigurement. The importance attached to this by people in endemica areas is reflected in the old practice of leishmanization, which involves deliberate and risky infection with Leishmania in order to induce life-long immunity at the price of an ulcer and lesion on less exposed parts of the body.

[0008] During their life cycle, Leishmania grow in diverse environmental conditions, and differentiate through distinct developmental stages (see reviews Wilson 1990, Smith et al., 1994). In the sandfly vector, they grow as slender, flagellated infectious promastigotes. When the sandfly takes a blood meal, the parasites are transmitted to the human host where they are phagocytosed by resident skin macrophages. Within the macrophage lysosome, the parasites differentiate into round, non-flagellated amastigotes where they replicate until the macrophage is lysed. They are then released to infect other macrophages, or are taken up by a sandfly where they differentiate back to the promastigote stage to repeat their life cycle.

[0009] Life long protection achieved by natural or deliberate infection with Leishmania suggests that mass vaccination against this disease is feasible. Progress has been made in human clinical trials using whole killed parasites in vaccines against cutaneous leishmaniasis. However, problems have arisen such as the unavailability of reagents or variations in the host response to challenge infection. Furthermore, subcutaneous vaccination with heat-killed, avirulent or radio-attenuated promastigotes has often been ineffective or worse, exacerbated lesions. Thus, to avoid the risk of exacerbating naturally acquired infections by vaccination, it is essential to develop second generation vaccines, e.g. to use immunologically purified antigen(s) or derivative(s).

[0010] The clinical manifestations of human leishmaniasis can be mimicked in various inbred mouse strains following infection with L.major. The majority of strains (e.g. CBA, C57BL/6) are relatively resistant to infection, developing only small lesions at the site of parasite inoculation, which are self-healing within a few weeks. In contrast, susceptible strains such as BALB/c mice develop severe cutaneous lesions with no tendency to resolve and eventual fatal visceralization of the infection. In experimental murine leishmaniasis, it is generally accepted that CD4⁺ T cells are responsible for resistance to infection with L.major, although CD8⁺ lymphocytes have also been shown to play a role in the immunity against this parasite (Muller et al., 1989, Hill et al., 1989). Animal model studies have led to the delineation of two defined CD4⁺ T lymphocyte subsets, Th1 and Th2, which may in part determine the outcome of L.major infection. Detailed discussions on the importance of the Th1/Th2 balance and the cytokine network(s) have been reported in recent reviews (Liew and O'Donnell, 1993; Milon et al., 1995). Briefly, the Th1 response is associated with the production of the cytokines IL-2 and γ-IFN, parasite killing, healing and protection, while the Th2 response is associated with the production of IL-4 and/or IL-10, disease progression and susceptibility (Heinzel et al., 1991; Scott, 1989). This pattern of lymphokine production has also been observed in human leishmaniasis (Reed and Scott, 1993). More recently, involvement of IL-12 in the immune response to Leishmania has been reported. IL-12 facilitates the development of a Th1 response by stimulating the production of γ-IFN and down-regulating that of IL-4 (Heinzel et al, 1993; Sypek et al, 1993).

[0011] Many studies using Leishmania major promastigotes derived antigens, such as the surface membranes gp63 and lipophosphoglycan (Russell et al, 1988), soluble extract (Scott et al, 1987) or gp63 epitopes (Yang et al, 1991) have shown that protection can be achieved at various levels in the susceptible BALB/c mice. Similarly, for example dp72 and GP46/M2 have been used against Leishmania donovani and Leishmania amazonensis respectively, but only partical protection has been observed (Rachamim and Jaffe, 1993; McMahon-Pratt et al, 1993).

[0012] In these trials, only promastigote derived antigens were used. In the research that led to the present invention it was conceived that vaccines comprising antigens present in different stages of the life cycle of the parasite might increase the percentage of protection. Furthermore, it was found that some proteins are exported as peptides to the macrophage surface and are involved in T-cell mediated immune response towards intracellular parasites. Such parasite antigen(s) involved in inducing protective immunity have not previously been identified. The identification and characterization of such gene products are imperative to allow an understanding of intracellular parasitism as well as the design of diagnostic tests and vaccines.

[0013] It is therefore the object of the present invention to provide genes and their derivatives like mRNA or proteins, that may prove to be useful in diagnosis, prophylaxis and treatment of infection by intracellular infectious agents like parasites, in particular trypanosomatids, like Leishmania species.

[0014] In the reasearch that led to the invention it was surprisingly found that intracellular proteins of the trypanosomatids in general and Leishmania in particular are capable of inducing immunity against the corresponding parasite species. This was in particular found for histones of these parasites.

[0015] The invention pertains to the general finding that intacellular antigens (e.g. histones) that are already involved in the T-cell mediated immune response towards intracellular parasites are a good starting point for the design and development of vaccines, pharmaceuticals and diagnostic tests. In the following this principle will be illustrated by reference to trypanosomatids in general and Leishmania species in particular.

[0016] The invention in its most basic form thus provides for trypanosomatid histones in substantially isolated form for use as a protective antigen against trypanosomatid infection. The histones may be isolated from the corresponding parasite species but are preferably produced by means of recombinant DNA techniques.

[0017] For the latter approach the invention also provides genes encoding the protective histones. Common to these genes is their ability to hybridise to:

[0018] a) at least a distinguishing part of the polynucleotide of the sequence depicted in FIG. 6A; or

[0019] b) those parts of the sequence of FIG. 6A that encode a part/parts of the histone that is/are responsible for the protective capacity of the polypeptide; or

[0020] c) the complementary strand of either a) or b).

[0021] From the above it follows that in its most basic form the recombinant histone may be the complete histone encoded by the gene isolated from the parasite species. In a more advanced embodiment only parts of the gene, either one or more, encoding one or more parts of the histone, at least some of which parts are responsible for its protective capacity, may be used.

[0022] The phrase “at least a distinguishing part of the polynucleotide” is intended to indicate that genes of the invention need not necessarily hybridise to the complete sequence depicted in FIG. 6A. The invention in fact provides for a gene family the members of which share a sequence similarity and the fact that they encode a histone, in particular histone H1. These two features will enable the skilled person to define the extent to which the sequence of FIG. 6A should hybridise to the other members of the family.

[0023] One possibility to establish whether a gene that has been isolated belongs to the family of the invention is comparison of its derived amino acid sequence with an amino acid database, such as the Swiss Prot database or the EMBL database. Such a database will give information on the homology of the derived amino acid sequence with known sequences. On the basis hereof the skilled person can establish whether he actually isolated a histone. A further tool in establishing whether a histone gene was isolated, is chemical and physical characterisation of the gene product. For example, histones are nuclear proteins and bind DNA.

[0024] The nucleotide sequence depicted in FIG. 6A is the sequence designated SW3 and already described previously. The invention is intended to encompass both the use of this gene and its derivatives and its family members as defined above.

[0025] Furthermore, the invention relates to derivatives of the genes, which derivatives comprise fragments of the gene, complete or partial cDNAs of the gene, complete or partial mRNAs to the gene, complete or partial proteins encoded by the gene, peptides comprising at least an immunogenic part of the protein, antisense oligo- or polynucleotides, fusion products between at least part of the gene, cDNA, mRNA, protein or peptide and at least part of another gene, cDNA, mRNA, protein or peptide, antibodies against the gene, cDNA, mRNA, protein, peptides or fusion products thereof, primers specific for the gene, cDNA or mRNA, wherein each derivative may either be isolated or may be obtained through recombinant DNA techniques. This list is not to be construed as limiting to the invention. For the skilled person the above will be a guide to define derivatives falling within the scope of the invention. These derivatives may be obtained by using commonly known and rather straightforward molecular biological techniques, described for example by Sambrook et al., 1989 (infra).

[0026] In this application “gene”, “cDNA”, “mRNA”, “oligonucleotide” and “polynucleotide” as well as their antisense or complementary counterparts may be referred to as “nucleic acids”.

[0027] “Proteins”, “peptides” or “polypeptides” refer to the products obtainable by transcription and translation of the nucleic acids and are generally referred to as “gene products”.

[0028] These derivatives can be identified by molecular hybridisation to the gene (for antisense polynucleotides or RNAs), by their activity, by their function, by recognizing the gene product or parts thereof (for antibodies), by the immune system as helper or cytotoxic T lymphocyte epitopes.

[0029] The invention further relates to expression vectors harboring the nucleic acids for producing mRNA or gene products. Again the skilled person will be very well capable of selecting a suitable vector and the necessary expression signals, such as transcription and translation initiation and termination sequences based on his common knowledge and the information contained in this application.

[0030] According to a further aspect thereof the invention provides for probes directed against the nucleic acids, antibodies directed against the gene products, nucleic acid molecules or polypeptides recognising the amino acid sequence of the gene products. The gene product is a nuclear protein that may be isolated due to the fact that it binds to DNA.

[0031] Furthermore, the invention provides for diagnostic agents comprising said nucleic acids, antibodies or said gene products for use in assaying infection and thus diagnosing Leishmania infections, and the use of said nucleic acids, antibodies or said gene products for prophylactic purpose, e.g. as component in a vaccine, or in therapy.

[0032] In particular this invention relates to intracellular protein, in particular to nucleic acid binding protein, more in particular to nuclear proteins. In particular, this invention relates to histones, and more in particular to histones H1, in particular to histone H1 gene family, isolated by molecular hybridisation or polymerase chain reaction, more in particular to the polypeptide of the SW3 gene.

[0033] The gene products, in particular products of the SW3 gene of Leishmania major or SW3 analogs of other Leishmania species, were found to elicit a strong immune response and demonstrate protective capacities.

[0034] In this invention, an immune response in mice was elicited by injecting a recombinant protein derived from the gene. A specific protection was obtained when the protein was injected sub-cutaneously and animals were subsequently challenged with live parasites. Another example teaches a nuclear polypeptide sequence, histone H1, and its use in immunisation regimens. Cross-hybridising mRNAs were detected in other Leishmania species. More particular the SW3 polypeptide was expressed in E.coli as a recombinant protein by a fusion with glutathion S transferase (GST). Mice were immunised with purified GST-SW3 polypeptide. The raised antibodies recognised the injected product. Immunised mice were infected with Leishmania major. Specific recognition was observed and protective effect of the polypeptide was shown in challenge experiments.

[0035] The present invention is described in the above under reference to L.major. However, the invention is also intended to encompass further Leishmania species, such as species of the subgenus Leishmania, comprising the complex L.major, which only comprises L.major species, the complex L.donovani, comprising for example L.chagasi, L.donovani, and L.infantum, and the complex L.mexicana, comprising inter alia L.amazonensis and L.mexicana, as well as species of the subgenus Viannia, comprising the complex L.braziliensis, comprising L.braziliensis en L.peruviana and the complex L.quyanensis, comprising the species L.guyanensis and L.panamensis.

[0036] The invention is illustrated by the following example which should not be considered as limiting to the scope thereof.

EXAMPLE

[0037] 1. Materials and Methods

[0038] In the following example many techniques that are well known and accessible to those skilled in the art of molecular biology, protein chemistry, immunology and Leishmania biology are utilized. Such methods are not always described in detail. Enzymes are obtained from commercial sources and used according to the suppliers protocols. Bacterial media and current cloning techniques are described in Sambrook et al. (Molecular cloning: a laboratory manual, CSH press 1989).

[0039] 1.1. Culture of parasites promastigotes and isolation of amastigotes

[0040]Leishmania major promastigotes (strain LV39-MHRO/SU/59/P or MRHO/IR/75/ER) are cultivated at 26° C. in Dulbecco's modified Eagle medium (DMEM; Gibco-BRL) on a solid rabbit blood agar (Louis et al, 1979), supplemented with 10% fetal calf serum (Seromed) and gentamicin (10 μg/ml). Amastigotes were produced in vivo. BALB/c mice were injected subcutaneously in the hind footpad with 2 to 5×10⁷ parasites/ml of stationary phase promastigotes.

[0041] Alternatively, amastigotes were obtained by passing parasites in the back of Swiss nude mice. L.major amastigotes were purified from back lesions and extracted according to a described protocol (Glaser et al., 1990).

[0042] 1.2. Nuclei isolation

[0043] Promastigotes are transferred to a 50 ml Falcon tube and centrifuged 5 min at 270×g at 4° C. The pellet is resuspended in 10 ml of cold 1×PBS and transferred to a cold 15 ml Greiner tube and centrifuged as before. The pellet is resuspended in 2 ml of lysis buffer (140 mM NaCl, 1.5 mM MgCl₂, 10 mM Tris-HCl (pH 8.6), 0,5% NP-40) containing 40 μl of 200 mM vanadyl ribonucleoside complex (Berger and Birbenmeier, 1979) and vortexed during 10 seconds. Following a centrifugation during 3 min at 6000×g at 4° C., the pellet corresponding to the nuclear fraction and 2 ml of supernatant which can be further processed to extract cytoplasmic RNA, were obtained. The nuclear pellet is frozen in liquid nitrogen and stored at −70° C. Isolation of amastigotes nuclei was performed using a similar protocol.

[0044] 1.3. Total histones and histone H1 extraction

[0045] Histones are soluble in HCl and, among histones, H1 is selectively soluble in perchloric acid. Cells were collected, washed twice in 1×PBS and lysed in 140 mM NaCl, 1.5mM MgCl₂ 10 mM Tris-HCl (pH 8.6), 0,5% NP40. Nuclei were pelleted at 6000 g for 3 min (Kontron). Nuclei were resuspended in 1.25N HCl for total histone extraction or 5% perchloric acid for histone H1 recovery, vortexed for 30 seconds and mixed on a rotating wheel at room temperature for an hour. Insoluble proteins are pelleted at 7000 rpm for 5 min. HCl histone extracts were precipitated with 8 volumes ice cold acetone and H1 perchloric extracts with 8 volumes of cold ethanol. Samples were then centrifuged at 10.000 rpm for 15 min and the pellets were resuspended in sample buffer for analysis by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and the SW3 nature was confirmed by immunoblotting using α415 petide serum as the detecting antibody. α415 peptide serum is serum produced by immunisation of a rabbit with the 415 peptide described under 1.4.

[0046] 1.4. Production and purification of antibody

[0047] A peptide sequence:

[0048] (NH₂-MSSNSAAAAVSAATTSPQKS-COOH) (“415”) deduced from the SW3 cDNA and corresponding to the first twenty amino acids was synthesised. Peptide synthesis was performed according to the F-moc, t-butyl strategy for solid phase synthesis, as described by Merrifield (1986) and Atherion et al. (1988). The peptide was purified by gel filtration by using a Sephadex-G25 and its molecular weight was confirmed by mass spectrometry on an LDI 1700 Mass Monitor (Linear Scientific Inc., Reno, Nev.) and shown to be >90% pure. The lyophilized peptide was dissolved in 1×PBS at 2 mg/ml and injected into rabbits to raise specific antibodies (performed by Eurogentec SA, Belgium). The obtained serum was called “α415 peptide serum”.

[0049] 1.5. Parasite protein analysis and immunoblotting

[0050] Promastigotes were collected by centrifugation (10 min at 3000 revs/min at 4° C.), washed three times in 1×PBS and resuspended in gel sample buffer for SDS-PAGE (Lämmli, 1970). Amastigotes were isolated according to a published method (Glaser et al., 1990) and are then handled as described for promastigotes. Protein gel electrophoresis was performed as described. Routinely, the proteins from 3×10⁷ cells boiled in 1×Lämmli buffer for 5 min, and loaded in a 4 mm wide slot were separated by 15% SDS-PAGE. Proteins were electrotransferred onto nitro-cellulose (Immunoblots). Immunoblotting from SDS-polyacrylamide gels was carried out as described by Harlow and Lane (1988) and a 1:1000 dilution of the rabbit α415 peptide serum was added to the filter incubated overnight at room temperature. Goat anti-rabbit secondary antibody and peroxydase conjugated protein A were used and a chemiluminescence reaction substrate (Amersham) was used to reveal presence of reactive polypeptide(s).

[0051] 1.6. Isolation of the SW3 gene and SW3 homologues

[0052] cDNA of total L.major mRNA or genomic DNA isolated from LV39 strain was used as template in polymerase chain reaction in presence of the oligonucleotides:

[0053] S-SW3 (5′-cccgtcgacggatgtcctctaattc-3′) and:

[0054] A-SW3 (5′-agagtcgacctatgatgcgtcttcgggcacgt-3′) in a buffer containing 20 mM Tris-HCl (pH 8.3), 100 mM KCl, 3 mM MgCl₂, 2.5 mM of each of the dNTPs and one unit of Taq polymerase. Different amplified products cross-hybridising with SW3 were obtained and subcloned in pGemini vectors (Promega Inc.) The nucleotide sequence was determined and deduced amino acid sequences were compared to SW3 amino acid sequence (Fasel et al., 1994).

[0055] 1.7. RNA isolation and analysis

[0056] Cytoplasmic RNA of different Leishmania species was isolated as described previously (Fasel et al., 1994). 15 μg RNA were fractionated on 0.8% agarose gel and transferred to Genescreen plus membrane (NEN research products). Radioactive antisense probes were generated by in vitro transcription of SW3 cDNA inserted in p GEM-1/2 vectors containing T7 and Sp6 RNA polymerases promotors. Hybridisation and washing were carried out as described (Fasel et al., 1994).

[0057] 1.8. Sequence comparison

[0058] The amino acid sequences were compared to the Swiss Prot sequence data bank and the degree of similarity was assessed by using Multiple Sequence Alignment (http:/www2pasteur.fr/-takaia/MAcours/multalign.html)

[0059] 1.9. Expression of the SW3 in E.coli

[0060] The open reading frame SW3 was amplified by polymerase chain reaction from the construct pCRII-SW3 (Fasel et al., 1994) using the oligonucleotides:

[0061] S-SW3 (5′-cccgtcgacggatgtcctctaattc-3′) and:

[0062] A-SW3 (5′-aga gtcgacctatgatgcgtcttcgggcacgt-3′) in a buffer containing 20 mM Tris-HCl (pH 8.3), 100 mM KCl, 3 mM MgCl₂, 2.5 mM of each of the dNTPs and one unit of Taq polymerase. The nucleotide sequence in bold characters correspond to SalI restriction sites which can be used to insert the PCR product in the SalI site of an expression vector. Amplification was performed using the following cylces: 8 min at 98° C., 3 min at 60° C., 2 min at 72° C. followed by 33 cycles of one min at 94° C., 1.5 min at 60° C. and 2 min at 72° C. The fragment was inserted into the SalI site of the vector pGEX-KG (Guan and Dixon, 1991) in phase with the reading frame of the glutathion S-transferase (GST). E.coli (DH5 α) were transformed by electroporation and the orientation of the insert was determined by HaeIII restriction enxyme which generates a fragment of different length according to the orientation of the insert. Orientation and sequence of the insert was confirmed by double stranded DNA sequencing. The DNA construct named pGEX-KG-415 was further used to obtain expression of a fusion protein GST-SW3. An E.coli colony containing the pGEX-KG-415 plasmid was used to inoculate bacterial culture medium (2×TY) supplemented with 100 μg/ml of ampicilline and grown overnight at 37° C. An aliquot was diluted 1:50 in 200 ml of 2×TY containing 100 μg/ml of ampicilline and cultures at 37° C. in 200 ml of 2×TY to an optical density at 600 nm between 0.6 and 0.8 IPTG was added to a final concentration of 1 mM and the culture as incubated for two additional hours.

[0063] Purification protocol, adapted from Smith and Johnson, 1988 and Frangioni and Neel, 1993 is performed at 4° C. if not mentioned otherwise. Bacteria are collected by centrifugation 15 min 6000×g and washed once with 6 ml of STE (10 mM Tris (pH 8.0), 150 mM NaCl, 1 mM EDTA). Cells are resuspended in 6 ml of STE containing 5 mg/ml of lysozyme. 10 μl of DNase I at a concentration of 10 mg/ml are added to the mix and the solution is incubated 15 min on ice. Dithiothreitol and sarkosyl are added to final concentration of 5 mM and 1.5% respectively. Additional lysis is obtained by two sonication of 30 sec (Sonifier 250, Brandson). The lysate is centrifuged 10 min at 10.000×g and Triton X-100 is added to the supernatant at a final concentration of 1.4% before an incubation of 15 tot 30 min on ice. Fusion protein is then purified by gentle stirring the mix with agarose-glutation beads (Sigma, Nr.G-4510) in 1×PBS for 30 min at room temperature. Beads are sedimented by centrifuging during 5 min at 1000×g and washed 4 to 5 times with 1 ml of cold PBS. Finally fusion protein is eluted from the resin by resuspending the beads in a solution of 10 mM glutathion (pH 8.0) (Merck Nr 4090) and incubating them 10 to 30 min at room temperature with constant stirring. The mix is centrifuged 5 min at 500×g and the supernatant is transferred to a new tube. Elution is repeated 2 to 3 times and the supernatants are pooled. Aliquot of the preparation is analysed by SDS 10% PAGE as described by Lämmli (1970). Fusion protein can be quantified by measuring absorbance at 280 nm or by comparing intensity of the fusion protein after Coomassie R-250 staining with the staining of defined quantities of molecular weight markers.

[0064] 1.10. Immunisation protocols

[0065] Two×25 μl of a 1:1 sonicated mixture of incomplete Freund's adjuvant and, in 1×PBS, 2 mg/ml of either GST-415, 415 peptide or GST alone into BALB/c mice subcutaneously. After 4 weeks, a boost was performed with an equivalent material.

[0066] 1.11. Parasite challenging protocols

[0067] Infection was performed by inoculation of 2 to 5×10⁶ of infectious promastigotes into the right hind footpad, the left footpad serving as internal control. Growth of the lesion was measured every week using a calliper. The sizes of the footpads were plotted against the number of days post-infection.

[0068] 2. RESULTS

[0069] The SW3 gene has a higher expression at the RNA level in the intracellular amastigote stage as compared to the free-living promastigote stage. It encodes a protein with sequence similarity to an histone H1 protein and has been described as an histone H1-like protein (Fasel et al., 1994) but no evidence for it has been provided.

[0070] To characterize the SW3 gene product we generated a rabbit antiserum directed against a peptide (“415”) corresponding to the amino-terminus of the deduced amino acid sequence of SW3 (see Materials and methods) and analysed cytoplasmic or nuclear lysates of LV39 strain. In immunoblots of Leishmania major promastigotes, anti-415 rabbit serum specifically recognized a doublet of proteins of sizes ranging from 17 to 19 kDa in a nuclear extract (FIG. 1, lane d) but not in a cytoplasmic extract (FIG. 1, lane b), demonstrating the nuclear localisation and the existence of at least two related but different nuclear proteins. Detection of two reacting polypeptides is suggestive of presence of two SW3 related genes. No polypeptides of similar size are recognised by rabbit pre-immune serum (FIG. 1, lanes a and c).

[0071] Biochemical analysis of the SW3 polypeptide confirmed the histone nature of the encoded polypeptide. SW3 protein can be purified out of a nuclear fraction to a high degree using the histones (HCl) and histone H1 preparative (perchloric acid) method (FIG. 2, lanes b, d and f). No signal is present when the protein extracts are analysed with pre-immune serum (FIG. 2, lanes a, c and e).

[0072] Part of the protein was expressed in a bacterial expression system as a fusion protein with glutathion-S-transferase (GST). A product of the expected molecular weight can be detected after purification on a GST-agarose column (FIG. 3, lane c, indicated by arrow 1). Arrow 2 indicates GST-415 fusion protein containing GST linked to 50 amino acids of SW3. The purified recombinant protein mix was injected in susceptible mouse strains (BALB/c) to demonstrate its potential as a protective antigen in parasite challenge experiments. Groups of mice were immunized subcutaneously (at the basis of the tail) either with a mixture of recombinant protein GST-415 and incomplete Freund's adjuvant (FIG. 4, panel D), incomplete Freund's adjuvant alone (FIG. 4, panel A), or a mixture of GST and incomplete Freund's adjuvant (FIG. 4, panel B). The 415 synthetic peptide was also used (FIG. 4, panel C). Mice were infected with 2-5×10⁶ L.major infectious promastigotes in one hind footpad either one month or three months after immunisation. The development of lesions was monitored weekly by measuring the increase of footpad thickness compared to the uninfected contralateral footpad. In the animals injected with the GST-415 recombinant product or with the 415 peptide (FIG. 4, panels D and C, respectively), susceptibility to infection was overcome: although the lesion started to appear as a sign of infection, its growth was arrested and the size of the lesion diminished. Graphs showing the regression of the lesion in the right footpad of mice injected with the peptide 415 or GST-415, is given in FIG. 4. No regression is observed in mice immunised with IFA (panel A) or GST alone (panel B).

[0073] Amplification of Leishmania major of genomic DNA using primers S-SW3 and A-SW3 to the most 5′ and 3′ ends of the SW3 coding region has given rise to various PCR products (FIG. 5, lane a). Certain of these products have been subcloned and sequenced. Our sequencing data has confirmed that the sequenced cDNAs differ from SW3 within the open reading frame (deletion of blocks of amino acids). The sequence of two additional members (A3, P3) of the SW3 family is given in FIG. 6.

[0074] Such SW3 and SW3 related polypeptides are interesting if it can be used to control other Leishmania species. For this reason, search for cross-hybridising mRNA transcripts of various sizes have been detected in New World Leishmania species such as L.chagasi, L.guyanensis, L.panamensis and L.amazonensis (FIG. 7). This result provides evidence for presence of related genes and gene products in other Leishmania which could be used to obtain protection.

FIGURE LEGENDS

[0075]FIG. 1 Biochemical localisation of histone H1 by immunoblotting using a rabbit antiserum raised against the peptide 415 corresponding to the N-terminus of the SW3 gene product. Cytoplasmic (lanes a and b) or nuclear (lanes c and d) proteins of stationary phase Leishmania major promastigotes were separated on 12.5% SDS-polyacrylamide gels before immunoblotting and probing with rabbit antiserum α-415 (lanes b and d) or with rabbit preimmune serum (lanes a and c). A reference molecular weight (21 kDa) is indicated.

[0076]FIG. 2 Biochemical characterisation of the SW3 gene product. Western blot analysis of nuclei (lanes a and b) and of 0.1N HCl (lanes c and d) or 5% perchloric acid (lanes e and f) nuclear extract of stationary phase promastigotes with rabbit antiserum raised against peptide 415 (lanes b, d, and f) or with rabbit preimmune serum (lanes a, c, and f). Extracts were separated on 12.5% SDS-polyacrylamide gels before immunoblotting.

[0077]FIG. 3 Expression and purification of the fusion protein GST-415 in Escherichia coli. Proteins were separated on a 12.5% SDS polyacrylamide gel and stained with Coomassie blue. The samples were loaded as follows: lane a, purified glutathion-S transferase (GST); lane b, molecular weight markers (MW); lane c, purified fusion protein GST-415 (the full length product is indicated by arrow 1; arrow 2 indicates GST-415 fusion protein containing GST linked to amino acids of SW3 as a result of an internal proteolytic cleavage).

[0078]FIG. 4 Measurement of the size of the foot pads following infection with Leishmania major LV39 strain. BALB/c mice, immunised either IFA (Panel A), with GST (Panel B), with the 415 peptide (Panel C) or the GST-415 fusion protein (Panel D) were infected in the right hind foot pad (filled lozenge symbols) with LV39 parasites. The left foot pad (open lozenge symbols) is used as an internal control.

[0079]FIG. 5 Polymerase chain reaction on LV39 genomic DNA using S-SW3 and A-SW3 oligonucleotides (cf. Material and Methods). The samples were loaded as follows: lane a, amplification of LV39 genomic DNA using S-SW3 and A-SW3 oligonucleotides; lane b, negative control corresponding to an amplification in the presence of S-SW3 and A-SW3 but in absence of DNA template; lane c, positive control corresponding to an amplification of SW3 cDNA in the presence of S-SW3 and A-SW3.

[0080]FIG. 6 Comparison of nucleotide and amino acid sequences of SW3 and of two new alleles A3 and P3. Sequences are aligned to obtain maximum similarity using Multiple Sequence Alignment program.

[0081]FIG. 7 Northern blot analysis of SW3 cross-hybridising mRNAs in other Leishmania species. Panel A: schematic representation of the SW3 transcript, the SW3 gene and of the antisense SW3 riboprobe. Panel B: Cytoplasmic RNA isolated from promastigotes of L.major (lane a), L.guyanensis (lane b), L.panamensis (lane c), L.chagasi (lane d) and L.amazonensis (lane e) were separated on a 0.8% agarose gel, transferred to a nylon membrane and hybridised with a SW3 anti-sense riboprobe as shown in panel A.

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1. Trypanosomatid histones in substantially isolated form for use as a protective antigen against trypanosomatid infection.
 2. Histones as claimed in claim 1, wherein the trypanosomatid is a Leishmania species, for example of the subgenus Leishmania, comprising the species L.major, L.chagasi, L.donovani, L.infantum, L.mexicana, L.amazonensis, and species of the subgenus Viannia, comprising L.braziliensis, L.peruviana, L.guyanensis, L.panamensis, and the trypanosomatid infection leishmaniasis.
 3. Histones as claimed in claim 1, wherein the trypanosomatid is a Trypanosoma species, such as T.cruzi, T.brucei.
 4. Histones as claimed in any one of the claims 1 to 3, which histones are H1 histones.
 5. Leishmania gene encoding a histone polypeptide as claimed in claim 2 or 4, which polypeptide has a protective capacity against leishmaniasis, and wherein the gene has a nucleotide sequence that can hybridise with: a) at least a distinguishing part of the polynucleotide of the sequence depicted in FIG. 6A; or b) those parts of the sequence of FIG. 6A that encode a part/parts of the histone that is/are responsible for the protective capacity of the polypeptide; or c) the complementary strand of either a) or b).
 6. Leishmania gene as claimed in claim 5, characterized in that the gene originates from L.major and the coding region thereof has essentially the nucleotide sequence depicted in FIG. 6B, or the complementary strand thereof.
 7. Leishmania gene as claimed in claim 5, characterized in that the gene originates from L.major and the coding region thereof has essentially the nucleotide sequence depicted in FIG. 6C, or the complementary strand thereof.
 8. Derivatives of the Leishmania gene as claimed in claims 5-7, which derivatives comprise fragments of the gene, complete or partial cDNAs of the gene, complete or partial mRNAs to the gene, complete or partial proteins encoded by the gene, peptides comprising at least an immunogenic part of the protein, antisense oligo- or polynucleotides, fusion products between at least part of the gene, cDNA, mRNA, protein or peptide and at least part of another gene, cDNA, mRNA, protein or peptide, antibodies against the gene, cDNA, mRNA, protein, peptides or fusion products thereof, primers specific for the gene, cDNA or mRNA, wherein each derivative may either be isolated or may be obtained through recombinant DNA techniques.
 9. Derivative as claimed in claim 8, characterized in that the derivative is an antibody directed against the peptide having the amino acid sequence: NH₂-MSSNSAAAAVSAATTSPQKS-COOH.
 10. Leishmania genes and/or their derivatives as claimed in claims 5-9 for use in diagnosis, prophylaxis and therapy of parasite infections.
 11. Leishmania genes and/or their derivatives for the use as claimed in claim 10, characterized in that the parasite infection is a trypanosomatid infection, in particular a Leishmania infection.
 12. Leishmania genes and/or their derivatives for the use as claimed in claim 11, characterized in that the Leishmania infection is an infection by one or more of the Leishmania species selected from the group consisting of the subgenus Leishmania, consisting of L.major, L.chagasi, L.donovani, L.infantum, L.mexicana, L.amazonensis, and species of the subgenus Viannia, consisting of L.braziliensis, L.peruviana, L.guyanensis, L.panamensis.
 13. Use of Leishmania genes and/or their derivatives as claimed in claims 5-9 for the preparation of diagnostic tests, prophylactic compositions or therapeutic compositions for the treatment of parasite infections, in particular trypanosomatid infections, such as Leishmania infections, for example caused by one or more of the Leishmania species selected from the group consisting of the subgenus Leishmania, consisting of L.major, L.chagasi, L.donovani, L.infantum, L.mexicana, L.amazonensis, and species of the subgenus Viannia, consisting of L.braziliensis, L.peruviana, L.guyanensis, L.panamensis.
 14. DNA construct, comprising one or more of the genes as claimed in claims 5-7, or fragments or cDNAs thereof, or fusion products comprising at least part of the gene, operably linked to appropriate expression signals.
 15. Vector carrying a DNA construct as claimed in claim
 14. 16. Vector as claimed in claim 15, characterized in that the vector is the pGEX-KG-415 plasmid as defined in the description.
 17. Host organism harbouring a DNA construct as claimed in claim 14 and/or a vector as claimed in claims 15 and
 16. 18. Diagnostic test, comprising the usual reagents and materials and a diagnostic agent which is suitable for assaying the presence of an infectious agent in a subject and is selected from the genes as claimed in claims 5-7 or the derivatives as claimed in claim 8 or
 9. 19. Diagnostic test as claimed in claim 18, wherein the test is suitable for assaying the presence of an infectious agent in a body fluid of the subject.
 20. Vaccine composition comprising the usual carriers and/or adjuvants and at least one histone as claimed in claim 1-4 and/or one or more derivative as claimed in claim 8 or 9, which histone or derivative is capable of eliciting protective immunity in a subject receiving the composition.
 21. Histones as claimed in claim 1-4, obtainable by the method comprising the steps of: a) lysing cells of a trypanosomatid species to obtain a lysate; b) isolating nuclei from the lysate; c) resuspending the nuclei in an extraction medium, for example either a 0.5-2.5 N, preferably a 1.25 N HCl solution for obtaining total histones, or 1-10%, preferably 5% perchloric acid for obtaining histone H1, to obtain a histone solution; d) optionally removing insoluble proteins from the histone solution; e) precipitating the histones by adding a precipitation agent, for example an excess of cold acetone for total histone or cold ethanol for histone H1.
 22. Histones as claimed in claim 1-4 or 21 for use in diagnosis, prophylaxis and therapy of parasite infections, in particular trypanosomatid infections, such as Leishmania infections, for example caused by one or more of the Leishmania species selected from the group consisting of species of the subgenus Leishmania, consisting of L.major, L.chagasi, L.donovani, L.infantum, L.mexicana, L.amazonensis, and species of the subgenus Viannia, consisting of L.braziliensis, L.peruviana, L.guyanensis, L.panamensis.
 23. Histones as claimed in claim 21 for use as a starting point for isolating genes encoding protective antigens and/or derivatives of the genes.
 24. Use of one or more histones as claimed in claim 1-4 or 21 for the preparation of diagnostic tests, prophylactic compositions or therapeutic compositions for the treatment of parasite infections, in particular trypanosomatid infections, such as Leishmania infections, for example caused by one or more of the Leishmania species selected from the group consisting of species of the subgenus Leishmania, consisting of L.major, L.chagasi, L.donovani, L.infantum, L.mexicana, L.amazonensis, and species of the subgenus Viannia, consisting of L.braziliensis, L.peruviana, L.guyanensis, L.panamensis.
 25. Use of intracellular or nuclear proteins as protective antigens for the treatment and/or prophylaxis of parasite infections. 